Ask anyone in this gritty industrial border city and they'll tell you their theory of who is killing the women: a mass murderer or copycats, maybe even someone from across the border in El Paso; drug traffickers trying to put the authorities off their own trail; local police, which is why the crimes have yet to be solved; people stealing internal organs for the black market.

Indeed, residents here have had nine uncomfortable years to get carried away by theories as murders of young Mexican women mount  274 of them to date.

Now, an international coalition  Mexican women's groups led by American academics, politicians, and law enforcement officials  is demanding a multinational investigation into the slayings, saying it's time the local police accepted the help of US forensic experts, resources, and laboratories.

The coalition is also renewing pressure on the hundreds of Juarez-based, US-owned maquiladoras  the workplaces that draw thousands of young Mexican women who are the primary prey of the killer or killers. They want these factories to provide employees with safe working conditions  including more secure transportation for their women employees.

"We believe this is a binational crime," says Emma Perez, chair of the history department at the University of Texas at El Paso and cochair of the newly formed Coalition Against Violence Toward Women and Families on the Border.

"And because it's happening on an international border, it requires international involvement," she says. "How many more women have to be murdered for this to be taken seriously?"

Irma Josefina Gonzalez says she used to speculate on who could be responsible for the murders  until her own daughter ended up missing last October.

Now she just wants justice.

"We don't know how it will end, but we'll continue looking for who is guilty because it's not fair," she says in the small apartment she once shared with her 20-year-old daughter, Claudia.

The murders and accusations of police incompetence and possible collusion have left this Mexican border city with an acrid international reputation  and it's testing the limits of the new level of cross-border cooperation that's been touted by Presidents George Bush and Vicente Fox.

Local authorities say they've solved many of the cases and brought the killers to justice. They also contend that their city is in the spotlight unfairly; that many large cities have equivalent numbers of missing and murdered women that don't get as much attention.

"It's just bad luck that we are getting all the attention," says Elfego Bencomo Lopez, deputy state prosecutor for Chihuahua. He points to the limited media coverage in Vancouver, B.C., where police are investigating a pig farmer over the disappearance of 50 women since 1983.

But this border city is distinctive because of the sheer number of women attracted to Juarez's 340 factories that produce everything from toasters to jeans to auto parts for export north. About 70 percent of the workforce here is comprised of young women, largely coming from rural towns and with little big-city experience.

Waiting for the bus on a recent afternoon, Georgina Martinez is one such worker. She came to Juarez two years ago in search of a job and is now assembling toasters for $4 a day.

Young, skinny, and shy  with long, dark hair  Ms. Martinez has many of the same traits of the murdered maquiladora women. She says she is aware of the situation and admits she's frightened.

Ofthe 274 murders of women in Ciudad Juarez, only 76 are considered by Mexican and American authorities to be"serial crimes." Athird of those have been resolved," says Mr. Bencomo. "We are continuing to investigate the others."

As pressure mounts on police to solve the remainder of these cases  and stop further murders  accusations of misconduct multiply and calls for US involvement intensify.

Back in November, for instance, when Claudia Gonzalez's body was found alongside seven other women who'd been raped, murdered, and dumped in shallow graves on the outskirts of town, police quickly arrested two bus drivers.

Mario Escobedo Salazar, a lawyer who represented one of the drivers, accused investigators of torturing the men into confessing and turned over photos of bodies, apparently burned by torture. Four days after he announced plans to file a corruption complaint against the officers who arrested his client, Mr. Escobedo was shot and killed by Chihuahua State Judicial Police who said they mistook the lawyer for a dangerous fugitive.

The two bus drivers are still in jail awaiting trial, and nobody  including Claudia's mother Josefina  believes they did it. She is just one of many who have lost faith in the police.

"There's no confidence in the police here," says Esther Chávez Cano, director of Casa Amiga, the city's first and only women's shelter. "They are not interested in solving these cases because these women are young and poor and dispensable."

In addition, says Ms. Chávez, investigators don't have the skills or expertise necessary to solve these crimes. After nine years, they still don't have any DNA evidence or fingerprints, she says.

"We ask ourselves that question every day: Why don't they want the help of the United States?"

Indeed, in calling for Mexican federal officials to take over the investigation of the murders in February, the Inter-American Commission for Human Rights (an arm of the Organization of American States), cast doubt on the ability of local Mexican authorities to solve the crimes.

"There unarguably has been a certain degree of negligence; there has not been a complete effort" to investigate these murders, said Marta Altolaguirre, commission inspector.

However, Mr. Bencomo insists his investigators are "open to receiving assistance from foreign agencies."

But FBI officials in El Paso and Mexican federal investigators say their help has been refused.

For her part, Josefina Gonzalez returned with other volunteers January to scour the trash-strewn dirt lot where her Claudia's body was discovered three months earlier. Nearby, they found what investigators arguably should have found: Claudia's pants, folded up neatly inside a plastic bag, as well as undergarments, hair, and personal identification from some of the other murdered women.

Ms. Gonzalez sarcastically asks what more she can do to help police: Turn over the killer?

But it's not just police incompetence, activists agree. Federal officials on both sides need to take an active role in the investigation, maquiladora owners need to institute more safety measures, and female workers need to be educated about potential dangers.

Claudia Gonzalez, for instance, showed up four minutes late to work that October day and the doors to the maquiladora were locked. She never made it home.